<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>盒子外边框及边框塌陷问题</title>
    <style>
        .box1{
            width: 200px;
            height: 200px;
            background-color: chocolate;
            margin:100px;
        }
        .box2{
            width: 100px;
            height: 100px;
            background-color: skyblue;
            /* margin: 100px; */
        }
        /* overflow: hidden; */
    </style>
</head>
<body>
    <div class="box1"><div class="box2"></div></div>
</body>
</html>